New evidence has added support for the 'myth' that Viking sailors navigated with the help of a sunstone. In a paper published today in Philosophical Transactions of the Royal Society B, scientists say the polarising properties of the crystal may well have allowed the Vikings to deduce the position of the Sun, even when hidden behind clouds or fog, or below the horizon.

Perpetual daylight during the summer sailing season in the far north would have prevented them from using the stars as a guide to their positions, and the magnetic compass had yet to be introduced in Europe — in any case, it would have been of limited use so close to the North Pole.

But Viking legends, including an Icelandic saga centering on the hero Sigurd, hint that these sailors had another navigational aid at their disposal: a sólarsteinn, or sunstone.

The saga describes how, during cloudy, snowy weather, King Olaf consulted Sigurd on the location of the Sun. To check Sigurd's answer, Olaf "grabbed a sunstone, looked at the sky and saw from where the light came, from which he guessed the position of the invisible Sun". In 1967, Thorkild Ramskou, a Danish archaeologist, suggested that this stone could have been a polarizing crystal such as Icelandic spar, a transparent form of calcite, which is common in Scandinavia.

On a more skeptical note, the Nature article also notes the view of Sean McGrail, expert in ancient seafaring, that there still is no actual evidence to indicate that the Vikings did use crystals in this way: "You can show how they could be used, but that isn't proof," he says. "People were navigating long before this without any instruments."